No abstract

The skeletal muscle mass is known to be controlled by the balance between protein synthesis and degradation. The fractional rate of protein synthesis has been reported to decrease age-dependently from 1 to 4 weeks of age in the chicken breast muscle (pectoralis major muscle). On the other hand, age-dependent change of the fractional protein degradation rate was reported to be less in the skeletal muscle of chickens. These findings suggest that protein synthesis is age-dependently downregulated in chicken muscle. We herein investigated the age-dependent changes in protein synthesis or proteolysis-related factors in the breast muscle of 7, 14, 28, and 49-day old broiler chickens. IGF-1 mRNA level, phosphorylation rate of Akt, and phospho-S6 content were coordinately decreased in an agedependent manner, suggesting that IGF-1-stimulated protein synthesis is downregulated with age in chicken breast muscle. In contrast, atrogin-1, one of the proteolysis-related factors, gradually increased with age at mRNA levels. However, plasma N τ -methylhistidine concentration, an indicator of skeletal muscle proteolysis, did not coordinately change with atrogin-1 mRNA levels. Taken together, our results suggest that the IGF-1/Akt/S6 signaling pathway is age-dependently downregulated in the chicken breast muscle.

We investigated the effects of dietary β-1,4-mannobiose (MNB) on the weights of body, breast muscles, thighs, liver, and abdominal adipose tissue in growing broiler chicks to evaluate whether MNB can be used as a feed additive for broiler chicks. A total of 24 eight day-old male broiler chicks were allocated to two cages and fed a control diet or a 0.01% MNB-supplemented diet for 14 days. Dietary MNB significantly increased the relative weight of breast muscles, whereas the weights of the body, thighs, liver and abdominal adipose tissue were not affected. The myostatin mRNA level in the breast muscle was significantly reduced by MNB. Since myostatin is a negative regulator of myoblast proliferation and differentiation, it is possible that the downregulation of myostatin gene expression is involved in the increased breast muscle growth with MNB. The plasma 3-methyl histidine level, which is known to be a nonmetabolizable amino acid marker of myofibrillar protein catabolism, and the breast muscle atrogin-1 mRNA level, which is involved in protein catabolism, were not affected by dietary MNB. In addition, MNB did not affect protease mRNA levels in the breast muscles. These results suggest that MNB does not affect proteolysis in the breast muscles. All our findings suggest that MNB is a promising candidate feed additive to improve the meat yield of broiler chickens.

The utilization of copra meal as a feed ingredient is limited because it contains a high level of mannan. However, recent findings indicate that the effect of copra meal on growth performance in broiler chickens can be improved by the supplementation of mannanase in the diet. In the present study, we examined the effect of mannanase-hydrolyzed copra meal (MCM) on growth performance and muscle protein metabolism in growing broiler chickens (Gallus gallus domesticus). Forty 8-day-old male broiler chicks were assigned to two groups (four birds in each pen, five replicates) and fed either a commercial diet (as a control diet) or a diet containing MCM at 0.2% until 22 days of age. Dietary MCM significantly increased the weights of body, breast muscle, and thighs in chickens, whereas the weights of abdominal adipose tissue and liver were not affected. Cumulative feed intake was significantly increased by MCM. Dietary MCM significantly decreased plasma 3-methylhistidine level. The messenger RNA and protein levels of muscle protein metabolism-related factors were not altered by MCM. These findings suggest that the growth-promoting effect of MCM is related to the suppression of muscle proteolysis in growing broiler chickens.